In known fire alarm systems, fire detectors are distributed throughout a building, the fire detectors being networked together and monitored by a central controller. Monitoring the fire detectors involves transmitting a sequence of polling signals to each detector and receiving signals indicating the status of the detector. If the presence of a fire is detected then the central controller can transmit a signal to alarm sounders located at various points around the building. Such a system is disclosed in our GB-A-2178878 which is incorporated by reference herein.
The sounders emit an audible warning such as a high pitched tone or siren, indicative of the need to evacuate the building. A more specific audible warning, such as a verbal command to evacuate the building or part of the building, can also be generated. A number of voice messages may be pre-recorded and stored in a memory of the sounder, which can be triggered by the signal from the central controller. A disadvantage is that customising the system to suit a particular environment is difficult because the voice messages are pre-programmed and can only be accessed from an interface at the sounder.
It is desirable to include a voice communication capability in a building for fire-fighters to communicate to each other or to other occupants within the building. It is known to provide public address systems in a building for such a purpose. However, existing public address and intercom systems are discrete audio products, separate from any fire alarm systems. The public address system and fire alarm system therefore require separate installation and operation.
Where fire detectors and sounders draw power from the network which is usual, power conservation is an important consideration, particularly during an alarm condition when many devices are drawing power from the network simultaneously.
A further consideration in introducing extra functionality into fire alarm systems or other installations is backwards compatibility. It is desirable to allow existing equipment, which recognises existing transmission protocols, to function without the need for replacement.